TECHNICAL FIELD
[0001] The present invention relates to a noncontact power feeding apparatus and a noncontact
power feeding method.
BACKGROUND ART
[0002] EP 2 161 811 A1 discloses as closest prior art an inductive charger to inductively provide power
to one or more battery powered appliances. This known charger comprises two or more
primary coil pairs that are arranged in a circular pattern for enclosing one or more
secondary coils of the appliances. Besides, the appliance can be provided with a capacitor
that is arranged in series with the secondary coil to form a resonance circuit having
one or more resonant frequencies. The alternating voltage provided to the primary
coils will have a frequency substantially corresponding to one of said resonant frequencies.
[0003] An inductive power transfer system including a primary power supply having a primary
resonant circuit, and an inductive power pick-up having a pick-up resonant circuit
for receiving power from the primary power supply and supplying power to an electrical
load has been presented in
WO 2009/091267 A2. To increase or decrease the power available to the load, the resonant frequency
of the primary resonant circuit and/or the pick-up resonant circuit may be varied
by a control means.
[0004] A method of power transmission utilizing electromagnetic field resonance between
a power transmission side and a power reception side has been known as a noncontact
(wireless) power transmission technique. Here, multiple sets of resonant coils having
the same resonant frequency are provided on the power reception side so that the power
reception side can receive electric power transmitted from the power transmission
side reliably and sufficiently even when a stop position of a vehicle deviates from
a prescribed position (see paragraph [0094] and Fig. 10 of
JP 2009 106136 A).
SUMMARY OF INVENTION
[0005] However, since the multiple sets of the power reception resonant coils thus provided
have the same resonant frequency, there is a problem of deterioration in power transmission
efficiency when the resonant frequency for power reception or power transmission coils
being initially set up varies due to an external factor such as an environmental condition.
[0006] A technical problem to be solved by the present invention is to provide a noncontact
power feeding apparatus and a noncontact power feeding method, which are capable of
suppressing deterioration in power transmission efficiency in case of a relative variation
in the resonant frequency of a power transmission resonator or a power reception resonator.
[0007] This object is achieved by a noncontact power feeding apparatus according to the
teaching of claim 1 and a noncontact power feeding method according to the teaching
of claim 7.
[0008] As an aspect of the present invention, a noncontact power feeding apparatus comprises:
a power transmission resonator; and a power reception resonator configured to be magnetically
coupled with the power transmission resonator by magnetic field resonance. The power
transmission resonator is magnetically coupled with the power reception resonator
by the magnetic field resonance, whereby electric power is supplied from an electric
power source to the power reception resonator through the power transmission resonator.
One of the power transmission resonator and the power reception resonator has a predetermined
single resonant frequency, and the other one of the power transmission resonator and
the power reception resonator has the predetermined single resonant frequency and
a resonant frequency different from the predetermined single resonant frequency. Among
the resonant frequencies which the other one of the power transmission resonator and
the power reception resonator has, at least one resonant frequency is set within a
range of a half width of another resonant frequency adjacent to the one resonant frequency.
[0009] According to the present invention, even when the resonant frequency for one of the
power transmission resonator and the power reception resonator varies due to an external
factor or the like, it is still possible to transmit the power using the varied resonant
frequency because the other one of the power transmission resonator and the power
reception resonator has multiple resonant frequencies inclusive of the aforementioned
resonant frequency. Thereby, deterioration in power transmission efficiency can be
suppressed in case of a relative variation in the resonant frequency.
BRIEF DESCRIPTION OF DRAWINGS
[0010]
[Fig. 1] Fig. 1 is an overall configuration diagram showing a power feeding system
for an electric vehicle to which a first embodiment of the present invention is applied.
[Fig. 2] Fig. 2 is an electric circuit diagram showing a detailed configuration of
the power feeding system in Fig. 1.
[Fig. 3A] Fig. 3A shows a parallel LC resonant circuit and a graph of an impedance
characteristic thereof.
[Fig. 3B] Fig. 3B shows a serial LC resonant circuit and a graph of an impedance characteristic
thereof.
[Fig. 3C] Fig. 3C shows a pair of LC resonant circuits having different resonant frequencies
and a graph of impedance characteristics thereof.
[Fig. 4] Fig. 4(a) is a graph showing an impedance characteristic of a power transmission
coil 1 in Fig. 1 and Fig. 2, and Fig. 4(b) is a graph showing impedance characteristics
of a power reception coil 2 therein.
[Fig. 5] Fig. 5 is an electric circuit diagram showing another example of the power
transmission coil 1 and the power reception coil 2 in Fig. 2.
[Fig. 6] Fig. 6 is a graph showing another example of the impedance characteristic
of the power transmission coil 1 and the impedance characteristic of the power reception
coil 2 in Fig. 4.
[Fig. 7] Fig. 7 is a schematic diagram showing an example of winding pitches of the
power transmission coil 1 and the power reception coil 2 in Fig. 2.
[Fig. 8] Fig. 8 is a graph showing self-resonance characteristics of the power transmission
coil 1 and the power reception coil 2 in Fig. 7.
[Fig. 9] Fig. 9 is a schematic diagram showing still another winding example of the
power transmission coil 1 and the power reception coil 2 in Fig. 2.
[Fig. 10] Fig. 10 is a perspective view showing another layout example of the power
transmission coil 1 and the power reception coil 2 in Fig. 1.
[Fig. 11] Fig. 11 is an electric circuit diagram showing another detailed configuration
example of the power feeding system in Fig. 1.
[Fig. 12] Fig. 12 is an electric circuit diagram showing still another detailed configuration
example of the power feeding system in Fig. 1.
[Fig. 13] Fig. 13 is an electric circuit diagram showing yet another detailed configuration
example of the power feeding system in Fig. 1.
[Fig. 14] Fig. 14 is a graph showing a resonance characteristic of a power reception
coil 2 in Fig. 12.
[Fig. 15] Fig. 15 is an electric circuit diagram showing other configuration examples
of the power transmission coil 1 or the power reception coil 2 in Fig. 1.
DESCRIPTION OF EMBODIMENTS
[First Embodiment]
[0011] A first embodiment of the present invention will be described below on the basis
of the drawings. In the drawings, the same constituents are denoted by the same reference
numerals, and duplicate explanation will be omitted. Fig. 1 is an overall configuration
diagram showing a power feeding system for an electric vehicle to which a first embodiment
of the present invention is applied, in which the present invention is embodied as
a power feeding system for supplying electric power to a driving motor MT of an electric
vehicle V.
[0012] A power feeding apparatus 10 of the embodiment includes a high-frequency alternating-current
power source 6, a primary coil 4, a power transmission coil 1, a power reception coil
2, a secondary coil 5, a rectifier 7, and an electrical storage device 8. Of the power
feeding apparatus 10, the power reception coil 2, the secondary coil 5, the rectifier
7, and the electrical storage device 8 are provided in the electric vehicle V, while
the high-frequency alternating-current power source 6, the primary coil 4, and the
power transmission coil 1 are provided outside the electric vehicle V. A power feeding
spot is an example of the outside of the electric vehicle V.
[0013] Here, the driving motor MT is connected to a driving system (a power train) of the
electric vehicle V. The driving motor MT generates a vehicle driving force upon receipt
of electric power from the electrical storage device 8, and outputs the generated
vehicle driving force to wheels via the driving system. Thereby, the electric vehicle
V travels. Meanwhile, in the case of using an alternating-current motor as the driving
motor MT, a power converter such as an inverter, which is not illustrated in Fig.
1, is provided between the electrical storage device 8 and the driving motor MT.
[0014] The power reception coil (a secondary self-resonant coil) 2 provided on the electric
vehicle V is formed of LC coils each having two open (unconnected) ends, and is magnetically
coupled with the power transmission coil (a primary self-resonant coil) 1 of the power
feeding apparatus 10 by magnetic field resonance. Thus, the power reception coil 2
can receive alternating-current power from the power transmission coil 1. Specifically,
the number of turns, the thickness, and the winding pitch of the power reception coil
2 are set as appropriate based on various conditions including a voltage of the electrical
storage device 8, a power transmission distance between the power transmission coil
1 and the power reception coil 2, resonant frequencies of the power transmission coil
1 and the power reception coil 2, and the like. The number of turns, the thickness,
and the winding pitch of the power reception coil 2 are set so as to achieve a large
Q value indicating resonance strength between the power transmission coil 1 and the
power reception coil 2 as well as a large κ value indicating the degree of coupling
therebetween. A configuration of the power reception coil 2 including the setting
of the resonant frequencies will be described later.
[0015] The secondary coil 5 is a one-turn coil whose two ends are connected to rectifier
7, and is capable receiving the electric power from the power reception coil 2 by
electromagnetic induction. It is preferable that the secondary coil 5 be located coaxially
with the power reception coil 2. The secondary coil 5 is provided in order to avoid
a variation in a self-resonant frequency of the power reception coil 2. The secondary
coil 5 outputs the electric power received from the power reception coil 2 to the
rectifier 7.
[0016] The rectifier 7 rectifies the high-frequency alternating-current power received from
the secondary coil 5, and outputs the rectified power to the electrical storage device
8. Here, instead of the rectifier 7, it is also possible to use an AC/DC converter
configured to convert the high-frequency alternating-current power received from the
secondary coil 5 into direct-current power. In this case, a voltage level of the direct-current
power is set equal to a voltage level of the electrical storage device 8.
[0017] The electrical storage device 8 is a chargeable and dischargeable direct-current
power source which is formed of a secondary cell using lithium ions or nickel-metal
hydride. The voltage of the electrical storage device 8 is in a range from about 200
to 500 V, for example. The electrical storage device 8 is capable of storing the electric
power supplied from the rectifier 7, and moreover, of storing regenerated power that
is generated by the driving motor MT. Then, the electrical storage device 8 supplies
the stored power to the driving motor MT. Here, a large-capacity capacitor may be
used as the electrical storage device 8 in place of or in addition to the secondary
cell. The electrical storage device 8 only needs to be an electric power buffer which
is capable of; temporarily storing the electric power from the rectifier 7 or the
driving motor MT; and supplying the stored electric power to the driving motor MT.
[0018] Meanwhile, the high-frequency alternating-current power source 6 installed on the
outside of the electric vehicle V (at the power feeding spot) includes a system power
source 6a (a commercial infrastructural alternating-current power source owned by
an electric power company), and a power converter 6b, for example. The power converter
6b converts alternating-current power received from the alternating-current power
source 6a into the high-frequency alternating-current power which can be transmitted
from the power transmission coil 1 to the power reception coil 2 on the electric vehicle
V, and supplies the high-frequency alternating-current power thus converted to the
primary coil 4.
[0019] The primary coil 4 is capable of transmitting the alternating-current power to the
power transmission coil 1 by electromagnetic induction, and is preferably located
coaxially with the power transmission coil 1. The primary coil 4 is provided in order
to avoid a variation in a self-resonant frequency of the power transmission coil 1.
Moreover, the primary coil 4 outputs the electric power received from the power converter
6b to the power transmission coil 1.
[0020] The power transmission coil 1 is installed in the vicinity of the ground at the power
feeding spot, for example. The power transmission coil 1 is formed of LC resonant
coils each having two open (unconnected) ends, and is magnetically coupled with the
power reception coil 2 on the electric vehicle V by magnetic field resonance. Thus,
the power transmission coil 1 is capable of transmitting the alternating-current power
to the power reception coil 2. Specifically, the number of turns, the thickness, and
the winding pitch of the power transmission coil 1 are set as appropriate based on
various conditions including the voltage of the electrical storage device 8 charged
by the power transmitted from the power transmission coil 1, the power transmission
distance between the power transmission coil 1 and the power reception coil 2, the
resonant frequencies of the power transmission coil 1 and the power reception coil
2, and the like so as to achieve the large Q value and the large κ value. A configuration
of the power transmission coil 1 including the setting of the resonant frequency will
be described later.
[0021] Fig. 2 is a circuit diagram further specifying the power feeding system shown in
Fig. 1. The power converter 6b shown in Fig. 1 can be materialized as a switching
power source as shown in Fig. 2, for example. The switching power source 6b in Fig.
2 includes: a rectifier circuit formed of multiple diodes and configured to rectify
the alternating-current power source 6a; and a chopper circuit provided with multiple
transistors and configured to generate the high-frequency alternating-current power
from direct-current power obtained by the rectification.
[0022] The primary coil 4 forms magnetic coupling M between the primary coil 4 and each
of the three LC resonant coils included in the power transmission coil 1, and thereby
transmits the alternating-current power generated by the power converter 6b to the
power transmission coil 1.
[0023] As shown in Fig. 2, the power transmission coil 1 includes the three LC resonant
circuits which are mutually connected in series, for example. Each LC resonant circuit
is set so as to have a single self-resonant frequency f0. Note that the self-resonant
frequency of each LC resonant circuit can be set by adjusting the coil shape and size
including the number of turns, the thickness, and the winding pitch of the coil.
[0024] In the meantime, the power reception coil 2 includes three LC resonant circuits L
21C
21, L
22C
22, L
23C
23 which are mutually connected in series, for example. The three LC resonant circuits
L
21C
21, L
22C
22, L
23C
23 are installed so as to be capable of receiving the alternating-current power transmitted
from the respective resonant circuits LC of the power transmission coil 1.
[0025] Meanwhile, the secondary coil 5 includes a coil L
R which forms magnetic coupling M between the secondary coil 5 and coils L
21, L
22, L
23 in the respective three LC resonant circuits L
21C
21, L
22C
22, L
23C
23. Thus, the secondary coil 5 is capable of receiving the alternating-current power
from the power reception coil 2. The rectifier 7 can be materialized by using a circuit
including multiple diodes for rectifying the received electric power. Thus, the alternating-current
power received by the three LC resonant circuits L
21C
21, L
22C
22, L
23C
23 is capable of being transferred to loads such as the electrical storage device 8
and the motor MT.
[0026] In Fig. 2, the alternating-current power source 6a and the power converter 6b constitute
a "structure including a switching power source"; the primary coil 4 and the power
transmission coil 1 constitute a "power transmission side resonator"; the power reception
coil 2 and the secondary coil 5 constitute a "power reception side multi-resonator";
and the rectifier 7 and the loads (8, MT) constitute a load circuit.
[0027] The principle of power transmission in accordance with the resonance method will
be described. The resonance method is the method of transmitting the electric power
wirelessly from one coil to another coil by bringing two LC resonant coils having
the same natural frequency into resonance through a magnetic field.
[0028] Specifically, as shown in Fig. 1, the high-frequency alternating-current power is
inputted from the high-frequency alternating-current power source 6 into the primary
coil 4. Thereby, a magnetic field is generated in the primary coil 4, and high-frequency
alternating-current power is generated in the power transmission coil 1 by electromagnetic
induction. Each of the power transmission coil 1 and the power reception coil 2 functions
as a LC resonant circuit using inductance L of the coil itself and stray capacitance
C between conductor wires. The power reception coil 2 has the same resonant frequency
as the power transmission coil 1, and is therefore magnetically coupled with the power
transmission coil 1 by magnetic field resonance. As a consequence, the alternating-current
power is transferred from the power transmission coil 1 to the power reception coil
2. Then, a magnetic field is generated in the power reception coil 2 upon receipt
of the alternating-current power. The magnetic field in the power reception coil 2
generates high-frequency alternating-current power in the secondary coil 5 by electromagnetic
induction. The alternating-current power in the secondary coil 5 is rectified to direct-current
power by the rectifier 7, and is then supplied to the electrical storage device 8.
[0029] In the meantime, a LC resonant circuit in which a capacitor C and a coil L are connected
in parallel is shown in an upper part of Fig. 3A, and an impedance characteristic
(frequency f - impedance Z) of the parallel LC resonant circuit is shown in a lower
part of Fig. 3A. In Fig. 3A, f
0 denotes the resonant frequency, and Δf denotes a half width of the resonant frequency.
In Formula (1) and Formula (2), "L" denotes inductance of the coil L, "C" denotes
stray capacitance between conductor wires of the coil L, and "R" denotes a parasitic
resistance value of the coil L.
[0030] [Expression 1]
[0031] As apparent from Formula (1) and Formula (2), the parasitic resistance becomes smaller
as a loss of the coil L becomes smaller. As a consequence, the half width Δf of the
resonant frequency becomes narrower, and the parallel LC resonant circuit therefore
exhibits a steep resonance characteristic.
[0032] A LC resonant circuit in which a capacitor C and a coil L are connected in series
circuit (also referred to as an antiresonant circuit) is shown in an upper part of
Fig. 3B, and an impedance characteristic (frequency f - impedance Z) of the serial
LC resonant circuit is shown in a lower part of Fig. 3B. The impedance characteristic
shown in Fig. 3B is different from that of Fig. 3A in that a minimum value appears
in Fig. 3B instead of a maximum point in Fig. 3A. For the rest, the serial LC resonant
circuit shown in Fig. 3B exhibits the similar impedance characteristic to that of
the parallel LC resonant circuit shown in Fig. 3A. Specifically, in the serial LC
resonant circuit, the parasitic resistance becomes smaller as the loss of the coil
L becomes smaller. As a consequence, the half width Δf of the resonant frequency becomes
narrower, and the serial LC resonant circuit therefore exhibits a steep resonance
characteristic.
[0033] Resonance means a state where a pair of LC resonant circuits set to have the same
resonant frequency exchange energy at high efficiency using the resonant frequency.
The inventors of the present invention have reached the following knowledge as a result
of extensive studies. Specifically, as shown in Fig. 3C, for example, even if a resonant
frequency f
01 of a LC resonant circuit L
1C
1 is different from a resonant frequency f
02 of another LC resonant circuit L
2C
2, the resonant circuits can still exchange energy at high efficiency like through
the resonance when ranges of their half widths Δf
1 and Δf
2 overlap each other.
[0034] Impedance characteristics of the power transmission coil 1 and the power reception
coil 2 are set as described below on the basis of the above-mentioned knowledge acquired
by the inventors. Fig. 4(a) shows an impedance characteristic of the power transmission
coil 1 and Fig. 4(b) shows an impedance characteristic of the power reception coil
2.
[0035] All the three LC resonant circuits constituting the power transmission coil 1 shown
in Fig. 2 include the coils L of the same type. The three LC resonant circuits therefore
have the same values of the inductance L of the coil L, the stray capacitance C of
the coil L, and the parasitic resistance R of the coil L. Accordingly, the power transmission
coil 1 has the single resonant frequency f
0, as shown in Formula (1). Here, it is preferable to use coils L having small parasitic
resistance R in order to enhance power transmission efficiency. When the parasitic
resistance R of the coils L is reduced, the half width Δf of the resonant frequency
becomes narrower as shown in Formula (2), and the parallel LC resonant circuit therefore
exhibits a steep resonance characteristic. As a result, it is possible to improve
safety because energy is not transferred to objects or electronic devices having resonant
frequencies outside the half width Δf.
[0036] In contrast, the three LC resonant circuits constituting the power reception coil
2 shown in Fig. 2 respectively include coils L of different types. The three LC resonant
circuits therefore have different values of the inductance L of the coil L, the stray
capacitance C of the coil L, and the parasitic resistance R of the coil L. Accordingly,
the power reception coil 2 has multiple resonant frequencies f
1, f
2, f
3, as shown in Formula (1). When a relationship among the three resonant frequencies
f
1, f
2, f
3 of the power reception coil 2 is defined as f
1 < f
2 < f
3, the resonant frequency f
0 of the power transmission coil 1 is preferably set to a frequency which at least
satisfies f
1 < f
0 < f
3.
[0037] Dashed lines in Fig. 4(b) show the respective impedance characteristics of the three
LC resonant circuits constituting the power reception coil 2. A solid line in Fig.
4(b) shows an overall impedance characteristic of the three LC resonant circuits combining
the impedance characteristics of the three LC resonant circuits together, which is
obtained as an outcome of resonance at the respective resonant frequencies f
1, f
2, f
3 of the LC resonant circuits. Since the three LC resonant circuits constituting the
power reception coil 2 have the different resonant frequencies f
1, f
2, f
3, a frequency characteristic (the half width Δf) of the LC resonant circuits on the
power receiving side as a whole can be made wider without increasing parasitic resistance
R of each of the coils L
21, L
22, L
23. Then, such a multi-resonance circuit having the widened frequency characteristic
is applied to the power reception side multi-resonator. As a consequence, even when
the resonant frequency f
0 of the LC resonant circuit on the power transmission side varies for some reason,
this LC resonant circuit will enter into resonance with one of the LC resonant circuits
on the power reception side. It is thus possible to transfer energy while suppressing
deterioration in power transmission efficiency.
[0038] In the meantime, the power transmission coil 1 shown in Fig. 2 includes the three
LC resonant circuits having the same resonant frequency f
0. This is because: the power reception coil 2 includes the three LC resonant circuits
set at the mutually different resonant frequencies f
1, f
2, f
3; and the power transmission coil 1 can be located as close to the these three LC
resonant circuits as possible. This makes it possible to suppress deterioration in
power transmission efficiency attributed to the distance between the power transmission
coil 1 and the power reception coil 2.
[Second Embodiment]
[0039] The number of the LC resonant circuits constituting any of the power transmission
coil 1 and the power reception coil 2 is not limited only to the example shown in
Fig. 2. For instance, as shown in Fig. 5, a LC resonant circuit constituting the power
transmission coil 1 may be formed of one coil L and one capacitor C. In this case,
it is preferable to increase a coil diameter so that the coil can be located as close
as possible to the multiple LC resonant circuits which constitute the power reception
coil 2. Here, the resonant circuits of the power reception coil 2 have to include
at least two LC resonant circuits in order to effect the multiple resonant frequencies.
[Third Embodiment]
[0040] In the power feeding system shown in Fig. 2, the resonant frequencies f
1, f
2, f
3 of the power reception coil 2 may be set as described below. Like Fig. 4(a), Fig.
6(a) shows the impedance characteristic of the LC resonant circuits constituting the
power transmission coil 1. Like Fig, 4(b), Fig. 6(b) shows the impedance characteristics
of the LC resonant circuits constituting the power reception coil 2. Specifically,
dashed lines in Fig. 6(b) show the respective impedance characteristics of the three
LC resonant circuits constituting the power reception coil 2. A solid line in Fig.
6(b) shows an overall impedance characteristic of the three LC resonant circuits obtained
by combining the impedance characteristics of the three LC resonant circuits together.
At least one of the resonant frequencies f
1, f
2, f
3 of the three LC resonant circuits is set within a range of the half width Δf of an
adjacent one of the resonant frequencies. Accordingly, the combined impedance characteristic
of the LC resonant circuits indicated with the solid line in Fig. 6(b) can be adjusted
to have a relatively flat characteristic within a predetermined frequency range. Thus,
it is possible to realize the relatively wide half width Δf while avoiding an increase
in the loss of the coil L attributed to an increase in the parasitic resistance R.
In the example of Fig. 6(b), each of the resonant frequencies f
1, f
2, f
3 of the three LC resonant circuits is set within the range of the half width Δf of
the resonant frequency adjacent thereto.
[0041] Operations of the electric circuits shown in Fig. 2 are as described below. Specifically,
the resonant frequency of the LC resonant circuits of the power transmission coil
1 is set at f
0, and the resonant frequencies of the three LC resonant circuits of the power reception
coil 2 are set at f
1, f
2, f
3, respectively. Moreover, f
2 is set equal to f
0, for example. In this case, the three LC resonant circuits of the power transmission
coil 1 enter into resonance with the LC resonant circuit in the middle having the
resonant frequency f
2 among the three LC resonant circuits of the power reception coil 2, and transfer
energy thereto at high efficiency. In the meantime, the range of the half width Δf
of the LC resonant circuit in the middle having the resonant frequency f2 overlaps
those of the LC resonant circuits on both ends each having the resonant frequency
either smaller or greater than f
2 (the resonant frequency f
1 or f
3). For this reason, the energy is transferred at high efficiency from the LC resonant
circuit in the middle having the resonant frequency f
2 to the LC resonant circuits on both sides. As a consequence, the energy can be efficiently
transferred from the entire LC resonant circuits of the power transmission coil 1
to the entire LC resonant circuits of the power reception coil 2.
[0042] As described above, the half widths Δf of the multiple LC resonant circuits constituting
the power reception coil 2 is set to overlap one another. Accordingly, even in case
of a variation in the resonant frequency f
0 of the LC resonant circuits of the power transmission coil 1, the alternating-current
power efficiently can be transmitted as long as the variation falls within a predetermined
range, i.e., within the range of the combined half width Δf (see Fig. 6) of the LC
resonant circuits constituting the power reception coil 2.
[Fourth Embodiment]
[0043] Fig. 7 shows the power transmission coil 1 and the power reception coil 2 to which
a fourth embodiment of the present invention is applied. Like the power feeding system
shown in Fig. 1, a power feeding system of the fourth embodiment includes the switching
power source 6, the primary coil 4, the power transmission coil (a LC resonant circuit)
1, the power reception coil (a LC resonant circuit) 2, the secondary coil 5, and the
load circuit 8. Each of the power transmission coil 1 and the power reception coil
2 uses a self-resonant circuit formed of self inductance L and stray capacitance C.
[0044] Moreover, in order to set the power transmission coil 1 in a single-resonance structure,
the power transmission coil 1 of the fourth embodiment employs a coil prepared by
winding a wire evenly (at a pitch a) as shown in Fig. 7. Since the wire is evenly
wound, stray capacitance factors between the pitches of the wire spread evenly whereby
the power transmission coil 1 exhibits a self-resonance characteristic of the single-resonance
structure as shown in Fig. 8. On the other hand, the power reception coil 2 employs
a coil prepared by winding a wire unevenly, or one prepared by gradually changing
wire pitches, for example. The wire pitches may change in a range from a-1.5d to a+1.5d,
for instance. Thereby, values of stray capacitance between the pitches of the wire
gradually change. As a consequence, the power reception coil 2 exhibits a multi-resonance
characteristic having a larger half width Δf, as shown in Fig. 8. In the example shown
in Fig. 7, the pitches of the wire of the power reception coil 2 define an arithmetic
series. However, the invention is not limited only to this configuration. A similar
effect can also be obtained by using a geometric series or a series having a form
of an inverse number of the geometric series, for example. Meanwhile, Fig. 9 shows
an example of the power reception coil 2 which is wound in a three-dimensionally uneven
manner. This configuration can also achieve similar operation and effect.
[Fifth Embodiment]
[0045] Fig. 10 is a perspective view showing the power transmission coils 1 and the power
reception coils 2 to which a fifth embodiment of the present invention is applied.
Each power transmission coil 1 of the fifth embodiment is a single-resonant coil prepared
by winding a wire evenly (at the pitch a) as shown in Fig. 7 or Fig. 9. The three
power transmission coils 1 are located in the vicinity of the ground of a power feeding
spot, for example, in positions respectively corresponding to the corners of an equilateral
triangle. Then, the electric power from the switching power source 6b is transmitted
to the power transmission coils 1 by electromagnetic induction M with the primary
coil 4.
[0046] In the meantime, each power reception coil 2 of the fifth embodiment is a multi-resonance
coil prepared by winding a wire in such a manner as to gradually change the pitches
within the range from a-1.5d to a+1.5d as shown in Fig. 7 or Fig. 9. The three power
reception coils 2 are located in the vicinity of a floor of the electric vehicle V,
for example, in positions respectively corresponding to the corners of an equilateral
triangle. Then, the electric power received by the power reception coils 2 is transmitted
to the load circuit 8 by electromagnetic induction M with the secondary coil 5.
[0047] In the fifth embodiment, the multiple power transmission coils 1 each prepared by
winding the wire evenly, and the multiple power reception coils 2 each prepared by
winding the wire in such a manner as to gradually change the pitches are arranged.
Thereby, even in case of a variation in the resonant frequency f
0 of the LC resonant circuit of any of the power transmission coils 1, the alternating-current
power can be efficiently transmitted as long as the variation falls within the predetermined
range, i.e., within the range of the combined half width Δf (see Fig. 6) of the LC
resonant circuits constituting the power reception coil 2. Furthermore, it is also
possible to suppress a reduction in power transmission efficiency attributable to
misalignment between the power transmission side and the power reception side. In
other words, since the multiple transmission coils 1 and the multiple reception coils
2 are provided, the reduction in power transmission efficiency can be suppressed even
when a stop position of the electric vehicle V deviates more or less from the power
feeding spot.
[0048] Although three power transmission coils 1 and three power reception coils 2 are provided
in the example shown in Fig. 10, the number of each coil is not limited only to three.
In addition, the number of the power transmission coils 1 and the number of power
reception coils 2 do not have to be equal to each other, but the numbers of the coils
may be different. Moreover, the layout positions of the three coils are not limited
to the corners of the triangle. The coils may be arranged in a front-back direction
or a widthwise direction of the electric vehicle V, for example.
[6th Embodiment]
[0049] Fig. 11 is an electric circuit diagram showing a power feeding system to which a
6th embodiment of the present invention is applied. In this embodiment, the primary
coil 4 for transferring energy from the switching power source 6b to the power transmission
coil 1 is omitted, and the power transmission coil 1 is connected directly to the
switching power source 6b. The power feeding system thus configured also exhibits
the operation and effect similar to those of the first to fifth embodiments. Furthermore,
the omission of the primary coil 4 brings about an effect that it is possible to achieve
lower costs, smaller sizes, and lower losses of the resonant circuits.
[7th Embodiment]
[0050] Fig. 12 is an electric circuit diagram showing a power feeding system to which a
7th embodiment of the present invention is applied. While the examples using the parallel
LC resonant circuits have been described for the first to 6th embodiments, the same
effect can also be obtained by using serial LC resonant circuits that exhibit an antiresonance
characteristic. Specifically, as shown in Fig. 12, the power reception coils 2 includes
three LC resonant circuits each formed by connecting a coil L and a capacitor C in
series, and the three serial LC resonant circuits are connected together in parallel.
Although the single-resonance parallel LC resonant circuits are used as the power
transmission coil 1, serial LC resonant circuits may be used as long as the circuits
have a single-resonance structure.
[8th Embodiment]
[0051] Fig. 13 is an electric circuit diagram showing a power feeding system to which an
eighth embodiment of the present invention is applied. The power transmission coil
1 or the power reception coil 2 may use a complex resonant circuit obtained by combining
a parallel LC resonant circuit and a serial LC resonant circuit. Fig. 13 shows an
example of the power reception coil 2 which is obtained by combining a parallel LC
resonant circuit and a serial LC resonant circuit having resonant frequencies which
are mutually different while falling within a range of a half width of each other.
Specifically, a coil L
2 and a capacitor C
21 constitute the parallel LC resonant circuit while the coil L
2 and a capacitor C
22 constitute the serial LC resonant circuit in Fig. 13.
[0052] It is to be noted that the secondary coil 5 for transferring the energy from the
power reception coil 2 to the load 8 is omitted in the example shown in Fig. 13. The
omission of the secondary coil 5 brings about an effect that it is possible to achieve
lower costs, smaller sizes, and lower losses of the resonant circuits. Moreover, the
primary coil 4 may also be omitted in the example shown in Fig. 13.
[0053] Fig. 14 shows a resonance characteristic of the complex resonant circuit which is
obtained by combining the parallel LC resonant circuit (a parallel resonant circuit)
and the serial LC resonant circuit (a serial resonant circuit). In Fig. 14, curves
indicated with dashed lines respectively represent the resonance characteristics of
the parallel resonant circuit and the serial resonant circuit while a curve indicated
with a solid line represents the resonance characteristic of the complex resonant
circuit.
[0054] The power transmission coil 1 or the power reception coil 2 may include any of resonant
circuits shown in Fig. 15(a) to Fig. 15(d). Fig. 15(a) to Fig. 15(d) are electric
circuit diagrams showing other configuration examples of any of the power transmission
coil 1 and the power reception coil 2, in which each reference sign L indicates a
coil while each reference sign C indicates a capacitor.
[0055] In the embodiments described above, the power transmission coil 1 is set at the predetermined
single resonant frequency f
0, and the resonant frequencies of the power reception coil 2 are set at the multiple
resonant frequencies f
1, f
2, f
3 inclusive of the resonant frequency f
0. Here, the configurations of the power transmission coil 1 and the power reception
coil 2 may be inverted. Specifically, in either the electric circuits shown in Fig.
2 or the electric circuits formed by inverting the power transmission coil 1 and the
power reception coil 2 in Fig. 5, the resonant frequency of the power reception coil
2 may be set at the predetermined single resonant frequency f
0 while the resonant frequencies of the power transmission coil 1 may be set at the
multiple resonant frequencies f
1, f
2, f
3 inclusive of the resonant frequency f
0.
[0056] It is to be noted, however, that power transmission efficiency is increased by setting
the single resonant frequency on the power transmission coil 1 side because it is
possible to prevent the power transmission coil 1 from entering into resonance with
an objected located near the power reception coil 2. In other words, the concentration
of power transmission energy from the power transmission coil 1 on the single frequency
makes it possible to minimize adverse effects on the area surrounding the power transmission
coil 1, and to minimize losses attributable thereto.
[0057] The power transmission coil 1 corresponds to a "power transmission resonator" and
"power transmission resonating means" according to the present invention. The power
reception coil 2 corresponds to a "power reception resonator" and "power reception
resonating means" according to the present invention. The high-frequency alternating-current
power source 6a corresponds to a "power source" according to the present invention.
The electric vehicle V corresponds to a "vehicle" according to the present invention.
A parallel or serial LC resonant circuit included in each of the power transmission
coil 1 and the power reception coil 2 corresponds to a "resonant circuit" according
to the present invention. The power transmission coil 1 and the power reception coil
2 correspond to a "pair of resonators" according to the present invention.
[0058] Although the embodiments of the present invention have been described above, it is
to be understood that the embodiments are described in order to facilitate understandings
of the present invention and are not intended to limit the scope of the present invention.
In this context, the constituents disclosed in the above-described embodiments should
also include all design changes and equivalents thereto which belong to the technical
scope of the present invention.
INDUSTRIAL APPLICABILITY
[0059] According to the present invention, even when the resonant frequency for one of the
power transmission resonator and the power reception resonator varies due to an external
factor or the like, it is still possible to transmit the electric power using the
varied resonant frequency because the other one of the power transmission resonator
and the power reception resonator has multiple resonant frequencies including the
aforementioned resonant frequency. Thereby, deterioration in power transmission efficiency
can be suppressed even in case of a relative variation in the resonant frequency.
Thus, the noncontact power feeding apparatus and the noncontact power feeding method
according to the present invention are industrially applicable.
1. Vorrichtung zur berührungslosen Leistungszufuhr, mit:
einem Leistungsübertragungsresonator (1); und
einem Leistungsempfangsresonator (2), der ausgebildet ist, magnetisch mit dem Leistungsübertragungsresonator
(1) durch Magnetfeldresonanz gekoppelt zu werden, wobei
der Leistungsübertragungsresonator (1) mit dem Leistungsempfangsresonator (2) durch
Magnetfeldresonanz gekoppelt ist, wodurch elektrische Leistung von einer elektrischen
Leistungsquelle (6a) über den Leistungsübertragungsresonator (1) dem Leistungsempfangsresonator
(2) zugeführt wird,
wobei einer des Leistungsübertragungsresonators (1) und des Leistungsempfangsresonators
(2) einen LC-Schwingkreis mit einer vorbestimmten einzigen Resonanzfrequenz (f2) aufweist,
und wobei der entsprechende andere des Leistungsübertragungsresonators (1) und des
Leistungsempfangsresonators (2) einen LC-Schwingkreis mit der vorbestimmten einzigen
Resonanzfrequenz (f2) und einen LC-Schwingkreis mit einer Resonanzfrequenz (f1, f3)
aufweist, die sich von der vorbestimmten einzigen Resonanzfrequenz (f2) unterscheidet,
dadurch gekennzeichnet, dass
von den mehreren Resonanzfrequenzen (f1, f2, f3) der LC-Schwingkreise, die der entsprechende
andere des Leistungsübertragungsresonators (1) und des Leistungsempfangsresonators
(2) aufweist, mindestens eine Resonanzfrequenz (f1, f3) eines LC-Schwingkreises auf
einen Bereich mit halber Breite (Δf) einer weiteren Resonanzfrequenz (f1, f3) festgelegt
ist, die benachbart zu der einen Resonanzfrequenz (f2) liegt.
2. Vorrichtung zur berührungslosen Leistungszufuhr nach Anspruch 1, wobei der eine des
Leistungsübertragungsresonators (1) und des Leistungsempfangsresonators (2) eine Spule
mit einem gleichmäßigen Windungsabstand hat.
3. Vorrichtung zur berührungslosen Leistungszufuhr nach Anspruch 1 oder 2, wobei der
entsprechende andere des Leistungsübertragungsresonators (1) und des Leistungsempfangsresonators
(2) eine Spule mit variierendem Windungsabstand aufweist.
4. Vorrichtung zur berührungslosen Leistungszufuhr nach einem der Ansprüche 1 bis 3,
wobei der eine des Leistungsübertragungsresonators (1) und des Leistungsumfangsresonators
(2) so zu viele Schwingkreise wie der entsprechende andere des Leistungsübertragungsresonators
(1) und des Leistungsumfangsresonators (2) aufweist, und
jeder der Schwingkreise des Leistungsübertragungsresonators (1) in der Nähe eines
entsprechenden der Schwingkreise des Leistungsumfangsresonators (2) angeordnet ist.
5. Vorrichtung zur berührungslosen Leistungszufuhr nach einem der Ansprüche 1 bis 4,
wobei der eine des Leistungsübertragungsresonators (1) und des Leistungsumfangsresonators
(2) der Leistungsübertragungsresonator (1) ist, und
der entsprechende andere des Leistungsübertragungsresonators (1) und des Leistungsumfangsresonators
(2) der Leistungsumfangsresonator (2) ist.
6. Vorrichtung zur berührungslosen Leistungszufuhr nach Anspruch 5, mit:
mehreren der Leistungsübertragungsresonatoren (1); und
mehreren der Leistungsumfangsresonatoren (2).
7. Verfahren zur berührungslosen Leistungszufuhr, mit:
magnetisches Koppeln eines Paar aus Resonatoren (1, 2) durch Magnetfeldresonanz, wobei
einer der beiden Resonatoren (1, 2) einen LC-Schwingkreis mit einer vorbestimmten
einzigen Resonanzfrequenz (f2) aufweist, und der andere der beiden Resonatoren (1,
2) mehrere LC-Schwingkreise mit mehreren Resonanzfrequenzen (f1, f2, f3), die die
vorbestimmte einzige Resonanzfrequenz (f2) beinhalten, aufweist, wodurch elektrische
Leistung von einer elektrischen Leistungsquelle (6a) über den einen Resonator (1,
2) zu dem entsprechenden anderen Resonator (1, 2) übertragen wird,
dadurch gekennzeichnet, dass
von den mehreren Resonanzfrequenzen (f1, f2, f3) der LC-Schwingkreise, die der entsprechende
andere des Leistungsübertragungsresontors (1) und des Leistungsumfangsresonatorsw
(2) aufweist, eine Resonanzfrequenz (f1, f3) eines LC-Schwingkreises mindestens auf
einen Bereich einer halben Breite (Δf) einer weiteren Resonanzfrequenz (f2) festgelegt
wird, die benachbart zu der einen Resonanzfrequenz (f1, f3) liegt.